This invention, referred to as either the Dugger Process (DP) or the Uniform Cation Distribution Process (UCDP), is a generic process for producing refractory metal hydroxyfluorides, metal oxyfluorides and refractory metal oxides. The reproducible oxides are produced as transparent or opaque, cationically-homogeneous, nanostructured and substantially pure compositions, at temperatures ranging from 100.degree. C. to 1537.degree. C. lower than the natural melting points of the oxides. For example, while magnesium oxide's melting point is 2852.degree. C., UCDP produces transparent magnesium oxide at 1315.degree. C.; a 1537.degree. C. temperature difference. Hence, this newly characterized product illustrates one of numerous novel and generic featured products and/or product improvements produced by the UCDP's irreversible chemical reaction of an oxide reactant to its oxide product.
More particularly, this invention relates to a generic process for producing, from small to commercial size quantities, refractory oxides of all compositional categories which include solid solution, undoped, doped, congruent melting, incongruent melting, stoichiometric and nonstoichiometric compositions as three-dimensional single crystalline, polycrystalline, glass and various type composite entities. In this invention, a composition refers to a compound, unless it is specified as a glass composition.
In this invention, a chemical complex is defined as: (1) at least one metal oxide chemically reacted with an aqueous hydrogen fluoride solution [HF(aq)] or its derivatives; or (2) at least one metal (cationic) fluoride chemically bonded to at least one oxygen anion, or to at least one hydroxyl group, or to at least one oxygen anion and one hydroxyl group. The chemical complex can display an excess of electrical charges. Therefore, metal hydroxyfluorides and metal oxyfluorides are chemical complexes. A HF(aq) derivative is a powder or granular mixture or solution in which hydrogen and fluoride ions are ingredients, i.e., ammonium hydrogen fluoride (NH.sub.4 HF.sub.2).
This invention, based on the Second Law of Thermodynamics, is operative because the below serial thermochemical shifting equilibria Reactions I-VA, by heat alone, proceed irreversibly to the right and render desired refractory oxide end products and volatile by-products. The Reactions' shifting chemical equilibria are indicative of precursors' formations or decompositions, as measured by the compositions' weight losses due to the volatile by-products reactions. Thus, the controlled serial thermochemical Reactions I-VA enable the complete conversion of a fully hydrated nanostructured metal fluoride and/or oxide to a metal hydroxyfluoride which decomposes into a metal oxyfluoride which decomposes into a refractory metal oxide end product. UCDP is the only process that produces all of the refractory oxide compositional categories.
The term "refractory oxide," is a metal oxide of ionic-covalent bonding. The efficacy of a refractory oxide's properties is principally a function of its starting materials and the process used to produce the oxide. These factors are controlled to obtain optimal reproducible end product properties.
Some of the major disadvantage-causal problems of the prior art refractory oxide production methods include: poor production reproducibility (reliability); random grain sizes; agglomerated powders which causes unintentional porosity and resulting low material densities; and, incomplete sintering reactions; volatilization of components as their melting points are approached with resulting uncontrollable cationic and anionic inhomogeneities (defects).
Conventional refractory oxide manufacturing, for example, requires high sintering temperatures for a given period of time to ensure an end product whose density closely approaches theoretical. For optimum results, this procedure is restricted to those solid state reactions whose reactants are thermally-stable throughout the reaction process, i.e., oxidative and/or vapor pressure state-wise. Also, harmful impurities can contaminate the prepared mixtures because of the powder-mixing procedures used. These restrictions and those earlier discussed in addition to a number of other constraints, limit present-day commercial manufacture to only a very few of the many compositional categories produced by the UCDP.
Prior art use of fluorides in thermohydrolytic procedures is different from the unique and novel UCDP. These differences are exemplified by the below prior art References 1-4 and 7-9.
1. Popov, A. I.; Knudson, G. E., "Preparation and Properties of the Rare Earth Fluorides and Oxyfluorides," J. Am. Chem. Soc., 76, Feburary 1954, p. 3921. PA0 2. Brixner, L. H., "Ferromagnetic Material Produced From Ferric Oxide And Barium Halide or Strontium Halide, And Process For Making Same," U.S. Pat. No. 3,113,109, Dec. 3, 1963. PA0 3. Messier, D. R.; Pask, J. A., "Kinetics of High Temperature Hydrolysis of Magnesium Fluoride: II, Influence of Specimen Geometry and Type and of Product Layers", J. Am. Cer. Soc., Vol 48, No. 8, September 1965, p. 459. PA0 4. Utsunomiya, T.; Hoshino, Y.; Sato, M., "Process of Hydrolysis Reaction from YF.sub.3 to Y.sub.2 O.sub.3 in a Humid Air at High Temperatures," Bulletin of the Tokyo Institute of Technology, No. 108, 1972. PA0 5. Bergna, H. E.; Iler, R. K., "Microcrystalline Corundum Powder, Sols Thereof, And Processes For Preparing Both," U.S. Pat. No. 3,370,017, February 20, 1968. PA0 6. Sellers, D. J.; Rhodes, W. H.; Vasilos, T., "Method Of Preparing Transparent Alumina," U.S. Pat. No. 3,899,560, Aug. 12, 1975. PA0 7. Dugger. C. O., "The Growth of Pink Magnesium Aluminate (MgAl.sub.2 O.sub.4) Single Crystals," J. of Electrochem. Soc., Vol 113, No. 3, March 1966, p. 306. PA0 8. Dugger, C. O., "Solution Growth of Oxidic Spinel and Other Oxide Single Crystals Following The Hydrolysis of Some Fluorides," J. of Phys. & Chem. of Solids Supplement, 1st Ed., Pergamon Press, New York, 1967, p. 493. PA0 9. Dugger, C. O., "Method For Growing Oxide Single Crystals," U.S. Pat. No. 3,595,803, July 27, 1971. PA0 Reaction I: YF.sub.3 hydration (ca. 20.degree. C. to ca. 95.degree. C.) EQU 2YF.sub.3 (p)+3H.sub.2 O(l).fwdarw.2[YF.sub.3 .multidot.1.5H.sub.2 O](c)+heat. PA0 Reaction II: Thermochemical reaction and shifting chemical equilibria produce a solid state yttrium hydroxyfluoride complex from ca. 150.degree. C. to ca. 900.degree. C. EQU 2[YF.sub.3 .multidot.1.5H.sub.2 O](c).fwdarw.Y.sub.2 (OH).sub.3 F.sub.3 (c)+3HF(g) PA0 Reaction IIA: Yttrium oxide-aqueous hydrogen fluoride solution reaction render simultaneous UCDP yttrium oxide processing and purification via recrystallization. EQU Y.sub.2 O.sub.3 (p)+3HF(aq).fwdarw.Y.sub.2 (OH).sub.3 F.sub.3 (c) PA0 Reaction III: Increasing temperature (&gt;600.degree. C.), thermochemical decomposition and shifting chemical equilibria of yttrium hydroxyfluoride complex produce a solid state oxyfluoride complex at ca. 1110.degree. C. EQU Y.sub.2 (OH).sub.3 F.sub.3 (c).fwdarw.[Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (c)+3H.sup.+ (g) PA0 Reaction IV: Chemical decomposition of yttrium oxyfluoride complex and shifting equilibria produce transparent yttrium oxide at ca. 1275.degree. C. over 15 hrs. EQU [Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (c).fwdarw.Y.sub.2 O.sub.3 (c)+3F.sup.- (g) PA0 Reaction V: Solid state yttrium oxyfluoride complex becomes molten at ca. 1430.degree. C. EQU [Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (c).fwdarw.[Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (m) PA0 Reaction VA: Molten or vapor phase isothermal [Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (m,v) decomposition-temperature & shifting equilibria at ca. 1430.degree. C.-1480.degree. C., preferably at 1470.degree. C., with programmed cooling to 1290.degree. C. over eight hours, produce transparent Y.sub.2 O.sub.3 crystals. EQU [Y.sub.2 O.sub.3 F.sub.3 ].sup.3- (m,v).fwdarw.&gt;Y.sub.2 O.sub.3 (c)+3F.sup.- (g) PA0 1. Write the appropriate chemical equations and calculate their reaction products' theoretical weight percent (wt. %) losses; PA0 2. Calculate and weigh a 100 gram batch of reagent grade or ultrapure reactants. PA0 3. Homogeneously dry-mix the reactants, then produce either a colloidal mixture by performing an acidic, neutral or basic pH liquid water slurry-blended dispersion, which produces either a fully-hydrated, cationically-homogeneous, nanostructured colloidal mixture, or a solution. PA0 4. Remove the liquid water from either the colloidal mixture or solution and form a dry product; pulverize and sieve (-200 mesh screen) the dried product (Reaction I); weigh from 3 to 7 grams to be processed for each run. PA0 5. Place the powdered composition in a pre-weighed empty crucible, weigh and program heat the crucible to a temperature and hold for several hours to react the mixture to a solid state hydroxyfluoride complex (Reaction II). PA0 6. Either during the heat treatment or at room temperature, weigh the crucible to determine the composition's wt. % loss. Pulverize and sieve the composition through a 325 mesh screen. X-ray analyze to determine the status of the precursor hydroxyfluoride complex. PA0 7. When the hydroxyfluoride complex phase reaction is complete, place the powdered composition in a pre-weighed empty crucible, weigh and heat the crucible to a Reaction III hydroxyfluoride decomposition-temperature for several hours. PA0 8. Either during the heat treatment or at room temperature, weigh the crucible to determine wt. % loss, pulverize, -325 sieve and X-ray to evaluate the status of the solid state oxyfluoride complex phase. PA0 9. When the oxyfluoride complex phase is complete, compact and heat from a Reaction IV through a VA oxyfluoride decomposition-temperature and hold several hours for solid, molten or vapor state production. Either during the heat treatment or at room temperature, weigh the crucible to determine wt. % loss, pulverize, sieve through a 325 sieve and X-ray to evaluate the reaction status of the solid state refractory oxide. PA0 10. Perform chemical, physical and infrared absorption analyses of the refractory oxide end product to determine if the reaction is complete, nanostructured and substantially pure. PA0 11. If residual oxyfluoride is present, heat treat the refractory oxide to a purification-temperature above the maximum oxyfluoride decomposition-temperature but below the refractory oxide's melting point, in either an air or an oxygen environment; hold for about eight hours. PA0 12. When the refractory oxide is substantially pure, an annealing at a given temperature may be required to impart a specific property, i.e., semiconductivity by means of a reducing gas.
Popov, Brixner, Messier and Utsunomiya, the first four references, all employed the same process of using a carrier gas to transport reactant water vapor to a second reactant which was either a metal (cationic) halide or metal oxyhalide to produce a metal oxide at temperatures ranging from 800.degree. C. to 1350.degree. C. As a function of the high temperature environment, chemical reactions between the metal halide/oxyhalide and water vapor reactants, caused the conversion of the halide/oxyhalide to the corresponding metal oxide and a gaseous hydrogen halide by-product. This type of chemical reaction process is referred to as a gaseous pyrohydrolytic reaction process; where "pyro" refers to heat and "hydrolytic" refers to the reaction of a substance with water or its ions.
On a commercial scale-basis to attain the efficacy of the UCDP water vapor could not duplicate most of the novel and numerous roles of liquid water neither chemically nor cost-effectively in the production of a refractory oxide. Because, for example, the quantitative water vapor effectiveness and the loss of water vapor of the gaseous pyrohydrolysis reaction process would be unreliable; an unknown amount of water vapor would be lost by evaporation before and during the reactant gaseous reactions. Thus, nonuniform water vapor phase hydrolysis of massive reactant quantities by the gaseous pyrohydrolysis would occur.
Bergna's (Ref. 5) prior art mechanical refractory oxide materials preparation procedures cause major materials and cost-effective disadvantages, as earlier discussed. The UCDP markedly reduces or eliminates these disadvantages.
Sellers' (Ref. 6) patent is a particularly specific and an extremely expensive procedure for producing one transparent Al.sub.2 O.sub.3 sample per run by the simultaneous application of heat (&gt;1800.degree. C.) and pressures (.gtoreq.3000 p.s.i.) without lateral constraints called "hot-forging." The UCDP eliminates this expensive procedure to manufacture transparent alumina.
Dugger (Ref. 7-9) used excess metal fluorides which served as both reactants and solvents to which he added given amounts of naturally occurring hydrated oxides as solutes to form molten solutions; which when slowly cooled, produced binary metal oxide single crystals. The purity and quality of the crystals ranged from good to poor because of solvent inclusions. The process was of low reliability, primarily because of insufficient hydration of the reactant metal fluorides with resultant low acceptable crystal yields; which were seldom reproducible.
In this invention, UCDP is a serial thermohydrolytic-reaction process where "thermo" indicates heat of reaction and/or furnace heating and "hydrolysis" is defined as a chemical reaction of a substance with liquid water or its ions (OH.sup.-, O.sup.= and H.sup.+) in the solid, liquid (molten) or vapor states.
The UCDP, a novel thermochemical commercial production procedure, is a marked improvement over the existing commercial refractory oxide production procedures and the refractory oxide research syntheses of the above references, because the UCDP markedly reduces or completely eliminates the restrictions or disadvantages of these exemplified procedures.
The chemistry of hydrogen fluoride (HF) is significantly different from the chemistry of hydrogen chloride (HCl), hydrogen bromide (HBr) or hydrogen iodide (HI); chemistry of the latter three acids are rather similar. Of the latter three, HCl is the most thermally stable. For example: (a) at 1000.degree. C., HF demonstrates much greater stability (&lt;&lt;&lt;% decomposition to H.sub.2 and F.sub.2) than the other acids; (b) HF's &lt;10% ionization (weak acid) vs. the other acid's &gt;93% ionization (strong acids); (c) HF's strong H--F bonding (d) strong HF bonding (polymerization) with water; (e) HF's 525% higher boiling point (20.degree. C.) over HCl's boiling point (-85.degree. C.); (f) HF reacts with most metals and metalloids.
On average, the melting and boiling points of fluorides and chlorides of the same cation are significantly different. For example, calcium fluoride's (CaF.sub.2) melting and boiling points are 1423.degree. C. and 2500.degree. C. and calcium chloride's (CaCl.sub.2) melting and boiling points are 782.degree. C. and &gt;1600.degree. C. Calcium oxide (CaO) melts at 2614.degree. C. The melting and boiling point temperature differences, respectively, between CaO and CaF.sub.2 are 1191.degree. C. and 350.degree. C. and between CaO and CaCl.sub.2 are 1832.degree. C. and 1250.degree. C. From the foregoing and laboratory experiments, the thermochemical properties of metal (cationic) fluorides are, by far, more stable and effective than metal chlorides in producing quality macroscopic three-dimensional (3-D) refractory oxides single crystals.
This applicant is unaware of any prior art that teaches or renders obvious, the use of metal fluorides as described in this invention. Of the four oxyhalides, only oxyfluorides thermochemically decompose into refractory oxides which exhibit the Novel (Inventive) Process Features of this invention.
While the UCDP is a process for producing a considerable number of high purity, high structural quality, reproducible yields of all of the refractory oxide compositional categories, there is some scientific uncertainty as to the actual precursor (intermediate) reactions that occur in thermochemically converting a hydrated metal fluoride to the corresponding refractory oxide end product; precursor metal hydroxyfluoride and metal oxyfluorides complexes are the intermediates reported in the literature. In this invention, therefore, it is assumed that all hydrated metal fluorides are thermochemically converted into precursor metal hydroxyfluoride and metal oxyfluoride complexes only, and the hydroxyfluoride and oxyfluoride complexes are considered to be low temperature (ca. &lt;900.degree. C.) and high temperature complexes, respectively. Other reactants used with hydrated metal fluorides include oxides, hydroxides, carbonates, nitrates, silicates, phosphates, selenates and sulfates. The stoichiometric amount of liquid water is determined and can be used but an excess amount is generally used to ensure the complete hydration of all reactants.
The UCDP differs from all other prior art refractory oxide manufacturing processes because it: (1) is a novel commercial thermochemical process for manufacturing refractory oxide of all compositional categories; (2) manufactures at novel reduced-temperatures, high structural quality, purity, and reproducible yields; (3) is the only commercial process which simultaneously manufactures and highly purifies compositions from the three states of matter [solid, liquid (molten) and vapor phase]; (4) markedly improves upon prior art refractory oxide manufacturing processes by: (a) replacing prior art average microstructured (10.sup.-6 meters) grain-sized compositions with nanostructured (10.sup.-9 meters) grain-sized compositions which significantly improve not only the numerous novel process and compositional inextricable-property-features but also refractory oxide applications; and (b) the portent of fabricating transparent, nanostructured geometrically-complex near net-shaped refractory oxide objects for high temperature applications with on-line, optical nondestructive evaluation (NDE) inspections.
The term "cationically-homogeneous" means that the refractory oxide's cations are uniformly distributed, i.e., with a compositional consistency of .gtoreq.99%, e.g., 99.5% or greater, preferably 99.9% or greater.
The term "nanostructured" material refers to the very small nanometer-size order of magnitude building structure of a material that includes grains, particles, filaments or layers of sizes less than 100 nanometers across.
The term "decomposition-temperature" refers to either a given temperature or a small temperature range within a larger temperature range wherein a precursor complex chemically decomposes by heat alone. The larger temperature range permits an oxyfluoride to include solid, molten and vapor oxyfluoride states; which from each state, a refractory oxide end product can be produced.
The term "substantially pure" refractory oxide as used herein means, based upon chemical analyses, the actual cationic composition differs by no more than about 3 wt. % from theoretical, preferably less than 1 wt. %, and most preferably, e.g., in the case of laser or superconductor oxides, 0.5 wt. % or less and the composition is substantially free of water, hydroxyl groups and deleterious impurities. UCDP compositions, which are insoluble in specific acids, salts or bases and contain deleterious impurities soluble in those acids, salts or bases, are powdered and the impurities removed by dissolution. The compositions are then again UCDP processed; beginning with Reaction IIA.